This invention relates to a method for detecting phosphorus segregates, and more particularly, to such a method capable of rapidly and easily detecting the distribution of phosphorus in continuously cast steel slabs or large-sized steel ingots.
Heretofore, segregation in large-sized steel ingots has been judged by sulfur printing. This method is by attaching photographic paper impregnated with aqueous sulfuric acid to a polished cross section of a large-sized steel ingot, thereby detecting hydrogen sulfide given off from segregated sulfur as stains on the photographic paper. This method has been widely used on the production line. Recently, however, steels subjected to low sulfide treatment and Ca treatment, such as steels resistant to hydrogen embrittlement cracking, have been put into practical use, and much progress has been made in the art to manufacture high purity steel and to prevent segregation in continuous castings. In such advanced steels having extremely low sulfur contents it is difficult to detect solidification segregates by the conventional sulphur printing.
Aside from the sulfur printing, a macroanalyzer is known as a device for examining the segregation of alloying elements. The macroanalyzer can quantitatively evaluate a planar section of a large-sized steel ingot by applying an electron beam to the section and detecting the spectrum of X-rays generated as in EPMA. However, this method is not applicable to a commercial production process because it uses an expensive device, the surface to be examined must be finished by emery paper of the order of #1,000, the measurement of a sample takes more than one hour, the configuration of a sample is limited, it cannot be applied to a wide section sample, and so on.
Accordingly it is an object of this invention to provide a novel improved method capable of rapidly detecting segregates in Ca-loaded steels and low-sulfide steels over a large surface area as easily as by the sulfur printing method. In this method, the element to be detected in place of sulfur is phosphorus, which has the great likelihood to segregate upon solidifying, and phosphorus segregates are detected on test paper as stains.
One known method of detecting phosphorus is the phosphor printing reported by M. Niessner in 1932. This method is by attaching filter paper which has been immersed in liquid B shown below in Table 1 to a surface of steel to be examined for 3-5 minutes, removing the paper from the steel surface, and thereafter dipping the filter paper into liquid A for 3-4 minutes, thereby producing a printed image. Beause of unclear printed images and low sensitivity, it is difficult to detect with this method phosphorus segregates in commercial grade steels. Also it requires an additional procedure of dipping the filter paper in another liquid after removal from a steel surface.
TABLE 1 ______________________________________ Liquid A Stannous chloride saturated solution 5 ml Concentrated hydrochloric acid 50 ml Water 100 ml Alum minor amount Liquid B Ammonium molybdate 5 g Water 100 ml Nitric acid (specific gravity 1.2) 35 ml ______________________________________
It is therefore, another object of the present invention to provide a novel method for detecting phosphorus segregation which takes the place of the conventional phosphor printing method, can produce a clear printed image with high sensitivity through an easy printing operation, and is suitable for use in the control of an in-place production process.